Nanostructural carbonous materials are being the focus of attention of research, due to the potential commercial applications and the novelty of their physical properties. The possibility of achieving properties of interest in macroscopic samples of carbon—such as long-lasting magnetic properties at room temperature—open a plethora of applications.
These materials may be used in magnetic imaging in medicine, or else applied in nanotechnology, communications, electronics, sensors, even biosensors, catalysis or separation of magnetic materials. However, for many years, the existence of pure carbon materials that could exhibit this type of property was difficult to believe.
Existing processes that lead to the obtainment of microscopic amounts of magnetic carbon use nuclear techniques (proton bombardment) or conditions of extreme temperature and pressure that make them unfeasible from the point of view of economy. In addition, they do not lead to materials having applicable ferromagnetic behavior when compared with the background magnetic signal (which, in general, is strongly diamagnetic).
In spite of the efforts for achieving magnetism in organic materials, very few systems proved to have this property. In the last few years, with the discovery of new allotropic forms of carbon, this field of research has been reviewed by the discovery of ferromagnetism in the charge transfer salt [TDAE]-C60 and in polymerized fullerene, as cited by P. M. Allemand et al, Science 253, 301 (1991), T. Makarova et al., Nature 413, 716 (2001) and R. A. Wood et al., J. Phys.: Condens. Matter 14, L385 (2002).
In addition, some papers show the existence of magnetization loops of the ferromagnetic type in highly oriented pyrolytic graphite (HOPG), as cited by Y. Kopelevich, P. Esquinazi, J. H. S. Torres, S. Moethlecke, J. Low Temp. Phys. 119, 691 (2000) and P. Esquinazi et al., Phys. REv. B 66, 24429 (2002).
Recently, two important papers showed, in a not ambiguous way, that the existence of ferromagnetism in pure carbon is possible. One of these papers, by P. Turek et al, Chem. Phys. Lett. 180, 327 (1991) reports the induction of magnetic orderings by proton irradiation on HOPG. This material shows magnetic ordering stable at room temperature.
Another paper reports the synthesis of a new allotropic form of carbon, a nanofoam totally consisting of carbon, which exhibits a behavior of the ferromagnetic type up to 90K, with a narrow hysteresis curve and high saturation magnetization, see A. V. Rode, E. G. Gamaly, A. G. Christy, J. G. Fitz Gerald, S. T. Hyde, R. G. Elliman, B. Luther-Davies, A. I. Veinger, J. Androulakis, J. Giapintzakis, Nature (2004). This material was prepared by ablation of vitreous carbon in argon atmosphere with high-repetition and high-power laser.
Also U.S. Pat. No. 6,312,768 deals with this subject, describing a method of depositing thin films of amorphous and crystalline nanostructures based on the deposition of ultra-rapid laser pulses.
However, despite the existing developments, there is still the need for a process of preparing magnetic graphitic materials in any amount, provided with long-lasting magnetic properties at room temperature, said materials being prepared from graphite and transition metal oxides, both powdered and under reaction conditions that lead to the desired product. Such process and the associated graphitic product are described and claimed in the present application.